Improving surface properties of iron sole plates for ensuring more comfortable ironing has always been a challenge in the relevant industry. For improving the surface properties, various coating materials such as Al—TiN, Teflon®, ferrous alloys, and other inorganic materials such as silanes and various ceramics have been proposed in the current state of the technical field. Al—TiN and Teflon, inter alia became preferable coatings for iron sole plates with allegedly low friction and non-sticking properties. It is well known in the art that these materials are applied to the external surface of the sole plates by various techniques such as PVD, CVD, spray coating and dip coating.
The present invention provides an alternative iron sole plate having a silane based coating layer which is advantageously produced by way sol-gel techniques. The inventive iron sole plate according to the invention is noted to be at least comparable with state of the art sole plates, and showing considerably improved characteristics in terms of cleaning, friction, fabric protection etc.
Sol-gel concept is known as a process comprising typically application of hydrolysable precursors such as oxides and alkoxides and a following heat treatment to obtain mechanically stable coating material with an enhanced density and hardness.
A coating method for glass, ceramic and metal surfaces using sol-gel technique aiming alkali-resistance, wear-resistance and dishwasher-safety for household, specifically kitchen appliances is introduced by the application WO 2010-072814-A1. The document explains a composite coating system applied on a metal surface to be protected, which are preferably aluminum and/or its alloys. The coating requires a porous base, which is an oxide layer, e.g. aluminum oxide layer established on the metallic base which is made of aluminum and/or its alloys. The said oxide layer is to be coated with two additional layers which require repetitive applications and heat treatments including cooling to the room temperature. First of them contains polydimethyl siloxane (PDMS) to obtain an elastic base to the second layer, which contains alkali metal compounds for alkali resistance. All those interlayers require additional process steps with their own costs including time-costs. Besides, this document is not concerned in acquiring low-friction and cleaning convenience at iron sole plates, instead the main concern of this document is stressed as chemical resistance by surfaces subjected to especially alkaline liquids.
Iron sole plates coated with sol-gel method is known per se by applications EP 0 998 604 B1 and US 2003/0074814 A1. Both of these documents explain methods using a plurality of coating layers applied to metal surfaces. Besides, the metallic base to be coated in both methods is essentially aluminum and/or its alloys, which requires a hard interlayer between the final coating layer and the base material itself. Therefore an oxide layer was employed as the interlayer, which means an additional process step with its own costs.
An iron sole plate which is made of aluminum and/or its alloys and coated using sol-gel method is presented in the document U.S. Pat. No. 6,901,687. This document does not clearly report the ingredients of coating solution, which also requires a porous aluminum oxide layer prior to the application of the liquid mixture. The dry thickness of the coating is 30-40 μm, which could readily cause potential cracks because of the great potential with inner tensions along this thick matrix.
An iron sole plate has its specific requirements to be used for a long lifespan without major problems. It is preferred for an iron sole plate to have an ironing surface with a rather high hardness which protects the sole plate from abrasive damages. Additionally, an iron sole plate should preferably cause low friction forces, thus a comfortable use during ironing. Moreover, because ironing is a high temperature application, there arises another expectation from an iron sole plate to have easy-to-clean properties due to accidental contamination of molten synthetic fabric materials which may stick, burn and cause burnt stains on the surface of the sole plate. The major objectives given hereinabove may generally be obtained by coating desired materials to the base surface. It is therefore, highly important for the industry of household appliances to have a coating composition that is applicable not only to limited kind of base materials (e.g. aluminum or aluminum alloys) but also other metallic structures such as stainless steel.